Java Basic _ Set List and Set interfaces, java Set listset

Java Basic _ Set List and Set interfaces, java Set listset

• Several Methods for listing collections need to be mastered
• AddFrist () adds an element to the first part of the set.
• AddLast () adds an element at the end of the Set
• RemoveFirst () removes the element of the first part of the set.
• RemoveLast () removes the elements at the end of the set.
• GetFrist () gets the element of the first part of the set.
• GetLast () gets the element at the end of the set.
• IsEmpty () determines whether the set is empty

• LinkedList<String> linkedList = new LinkedList<>();linkedList.add("a");linkedList.add("a");linkedList.add("b");linkedList.add("a");linkedList.addFirst("0");linkedList.addLast("9");System.out.println(linkedList);linkedList.removeLast();System.out.println(linkedList);linkedList.removeFirst();System.out.println(linkedList);String first = linkedList.getFirst();System.out.println(first);String last = linkedList.getLast();System.out.println(last);boolean b = linkedList.isEmpty();System.out.println(b);

•  

• Set interface (unordered, non-repeated)
• We can directly learn the HashSet interface.
• HashSet: When you store the same element, if it is not added, it will determine whether the collection exists. Here we use the custom reference type description.

• Package com. set; public class Person {private String name; private int age; public String getName () {return name;} public void setName (String name) {this. name = name;} public int getAge () {return age;} public void setAge (int age) {this. age = age;} public Person (String name, int age) {super (); this. name = name; this. age = age;} public Person () {super (); // TODO Auto-generated constructo R stub} @ Override public int hashCode () {final int prime = 31; int result = 1; result = prime * result + age; result = prime * result + (name = null )? 0: name. hashCode (); return result ;}@ Override public boolean equals (Object obj) {if (this = obj) return true; if (obj = null) return false; if (getClass ()! = Obj. getClass () return false; Person other = (Person) obj; if (age! = Other. age) return false; if (name = null) {if (other. name! = Null) return false;} else if (! Name. equals (other. name) return false; return true ;}@ Override public String toString () {return "Person [name =" + name + ", age = "+ age +"] ";}}

  Note that we need to overwrite the hashcld method and the equlas () method. Of course, we need to overwrite the toString () method during printing.

• Public static void main (String [] args) {HashSet <Person> hashSet = new HashSet <> (); hashSet. add (new Person ("Zhang San", 12); hashSet. add (new Person ("Li Si", 12); hashSet. add (new Person ("Zhang San", 12); hashSet. add (new Person ("Zhang San", 21); // System. out. println (hashSet); Iterator <Person> iterator = hashSet. iterator (); while (iterator. hasNext () {Person next = iterator. next (); System. out. println (next );}}}
  // Execution result: James 12
  Li Si 12
  Zhang San 21
  

   

• This means that the de-duplicated elements of HashSet are unordered.
• The Set interface also has a Set of sorted hashsets, which makes up for the unordered Set.

• Public class Demo02_LinkedHashSet {public static void main (String [] args) {LinkedHashSet <String> hashSet = new LinkedHashSet <> (); hashSet. add ("a"); hashSet. add ("B"); hashSet. add ("c"); hashSet. add ("d"); // enhanced for traversal for (String string: hashSet) {System. out. print (string + "");} // Iterator traverses iterator <String> Iterator = hashSet. iterator (); while (iterator. hasNext () {String str = iterator. next (); System. out. println (str);} System. out. println (hashSet );}